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Technical Paper

Improving Emissions, Noise and Fuel Economy Trade-Off by using Multiple Injection Strategies in Diesel Low Temperature Combustion (LTC) Mode

2010-10-25
2010-01-2162
Latest emissions standards impose very low NOx and particle emissions that have led to new Diesel combustion operating conditions, such as low temperature combustion (LTC). The principle of LTC is based on enhancing air fuel mixing and reducing combustion temperature, reducing raw nitrogen oxides (NOx) and particle emissions. However, new difficulties have arisen. LTC is typically achieved through high dilution rates and low CR, resulting in increased auto-ignition delay that produces significant noise and deteriorates the combustion phasing. At the same time, lower combustion temperature and reduced oxygen concentration increases hydrocarbon (HC) and carbon oxide (CO) emissions, which can be problematic at low load. Therefore, if LTC is a promising solution to meet future emission regulations, it imposes a new emissions, fuel consumption and noise trade-off. For this, the injection strategy is the most direct mean of controlling the heat release profile and fuel air mixture.
Journal Article

Effects of Methane/Hydrogen Blends On Engine Operation: Experimental And Numerical Investigation of Different Combustion Modes

2010-10-25
2010-01-2165
The introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap. This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR.
Journal Article

Comparison of Diesel Spray Combustion in Different High-Temperature, High-Pressure Facilities

2010-10-25
2010-01-2106
Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, high-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. For this paper, we describe results from comparative studies using constant-volume vessels at Sandia National Laboratories and IFP.
Journal Article

Cold Start on Diesel Engines: Effect of Fuel Characteristics

2010-05-05
2010-01-1506
Faced with the need to reduce greenhouse gas emissions, diesel engines present the advantage of having low CO₂ emission levels compared to spark-ignited engines. Nevertheless, diesel engines still suffer from the fact that they emit pollutants and, particularly nitrogen oxides (NOx) and particulates (PM). One of the most promising ways to meet this challenge is to reduce the compression ratio (CR). However a current limitation in reducing the diesel CR is cold start requirements. In this context, the fuel characteristics such as the cetane number, which represents ignition, and volatility could impact cold start. That is why a matrix of 8 fuels was tested. The cetane number ranges from 47.3 to 70.9 and the volatility, represented by the temperature necessary to distillate 5% of the product (T5%), ranges from 173 to 198°C. The engine tests were carried out at -25°C, on a common rail 4-cylinder diesel engine.
Journal Article

Increasing Power Density in HSDI Engines as an Approach for Engine Downsizing

2010-05-05
2010-01-1472
In the context of CO₂ emission regulations and increase of energy prices, the downsizing of engine displacement is a widely discussed solution that allows a reduction of fuel consumption. However, high power density is required in order to maintain the power output and a good driveability. This study demonstrates the potential to strongly increase the specific power of High Speed Diesel Injection (HSDI) diesel engines. It includes the technological requirements to achieve high specific power and the optimal combination of engine settings to maximize specific power. The results are based on experimental work performed with a prototype single-cylinder engine (compression ratio of 14). Tests were conducted at full load, 4000 rpm. Part load requirements are also taken into account in the engine definition to be compatible with the targets of new emission standards.
Journal Article

Optimization of a Euro 5 Vehicle Powered by an Ethanol Based Diesel Fuel

2010-05-05
2010-01-1520
Diversifying energy resources and reducing greenhouse gas emissions are key priorities in the forthcoming years for the automotive industry. Currently, among the different solutions, sustainable biofuels are considered as one of the most attractive answer to these issues. This paper deals with the vehicle application of an innovative diesel fuel formulation using Ethanol to tackle these future challenges. The main goal is to better understand the impact of using biofuel blends on engine behavior, reliability and pollutants emissions. This alternative oxygenated fuel reduces dramatically particulate matter (PM) emissions; this paves the way to improve the NOx/PM/CO₂ trade-off. Another major interest is to avoid adding a particulate filter in the exhaust line and to avoid modifying powertrain and vehicle hardware and therefore to minimize the overall cost to fulfill upcoming emission regulations.
Journal Article

Analysis of Combustion Process in Cold Operation with a Low Compression Ratio Diesel Engine

2010-04-12
2010-01-1267
Future emissions standards for passenger cars require a reduction of NOx (nitrogen oxide) and CO₂ (carbon dioxide) emissions of diesel engines. One of the ways to reach this challenge while keeping other emissions under control (CO: carbon monoxide, HC: unburned hydrocarbons and particulates) is to reduce the volumetric compression ratio (CR). Nevertheless complications appear with this CR reduction, notably during very cold operation: start and idle. These complications justify intensifying the work in this area. Investigations were led on a real 4-cylinder diesel 13.7:1 CR engine, using complementary tools: experimental tests, in-cylinder visualizations and CFD (Computational Fluid Dynamics) calculations. In previous papers, the way the Main combustion takes place according to Pilot combustion behavior was highlighted. This paper, presents an in-depth study of mixture preparation and the subsequent combustion process.
Journal Article

Study of Air Entrainment of Multi-hole Diesel Injection by Particle Image Velocimetry - Effect of Neighboring Jets Interaction and Transient Behavior After End of Injection.

2010-04-12
2010-01-0342
The air entrainment of multi-hole diesel injection is investigated by high speed Particle Image Velocimetry (PIV) using a multi-hole common rail injector with an injection pressure of 100 MPa. The sprays are observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a diesel engine during injection. Typical ambient temperature of 800K and ambient density of 25 kg/m3 are chosen. The air entrainment is studied with the PIV technique, giving access to the velocity fields in the surrounding air and/or in the interior of two neighboring jets. High acquisition rate of 5000 Hz, corresponding to 200 μs between two consecutive image pairs is obtained by a high-speed camera coupled with a high-speed Nd:YLF laser. The effect of neighboring jets interaction is studied by comparing four injectors with different numbers of holes (4, 6, 8 and 12) with similar static mass flow rate per hole.
Technical Paper

Modeling of Pollutant Emissions Using Combined Tabulated Detailed Kinetics and Reduced Kinetics

2010-04-12
2010-01-0628
In the context of low consumption and low emissions engines development, combustion processes modeling is a challenging subject as the requirements for accurately controlled pollutant emissions are becoming more stringent. From a scientific point of view, it is a major source of in-depth investigations as the chemical processes involved are strongly coupled to the flow characteristics. Among the various approaches developed recently to account for these processes in realistic configurations, tabulated techniques appear to be a promising way. They induce a good compromise between the accuracy of detailed chemistry and the computational time necessary to calculate complex configurations. Tabulation approaches were firstly developed to address the modeling of species concentrations in stationary combustors. They consist basically of pre-computed chemical kinetics using detailed mechanisms.
Technical Paper

Matching and Evaluating Methods for Euro 6 and Efficient Two-stage Turbocharging Diesel Engine

2010-04-12
2010-01-1229
While fuel efficiency has to be improved, future Diesel engine emission standards will further restrict vehicle emissions, particularly of nitrogen oxides. Increased in-cylinder filling is recognized as a key factor in addressing this issue, which calls for advanced design of air and exhaust gas recirculation circuits and high cooling capabilities. As one possible solution, this paper presents a 2-stage boosting breathing architecture, specially dedicated to improving the trade-off between emissions and fuel consumption instead of seeking to improve specific power on a large family vehicle equipped with a 1.6-liter Diesel engine. In order to do it, turbocharger matching was specifically optimized to minimize engine-out NOx emissions at part-load and consumption under common driving conditions. Engine speed and load were analyzed on the European driving cycle. The key operating points and associated upper boundary for NOx emission were identified.
Journal Article

Cold Operation with Optical and Numerical Investigations on a Low Compression Ratio Diesel Engine

2009-11-02
2009-01-2714
With a high thermal efficiency and low CO2 (carbon dioxide) emissions, Diesel engines become leader of transport market. However, the exhaust-gas legislation evolution leads to a drastic reduction of NOx (nitrogen oxide) standards with very low particulate, HC (unburned hydrocarbons) and CO (carbon monoxide) emissions, while combustion noise and fuel consumption must be kept under control. The reduction of the volumetric compression ratio (CR) is a key factor to reach this challenge, but it is today limited by the capabilities to provide acceptable performances during very cold operation: start and idle below −10°C. This paper focuses on the understanding of the main parameter’s impacts on cold operation. Effects of parameters like hardware configuration and calibration optimization are investigated on a real 4 cylinder Diesel 14:1 CR engine, with a combination of specific advanced tools.
Journal Article

Formation of Unburned Hydrocarbons in Low Temperature Diesel Combustion

2009-11-02
2009-01-2729
Low temperature combustion is a promising way to reach low NOx emissions in Diesel engines but one of its drawbacks, in comparison to conventional Diesel combustion is the drastic increase of Unburned Hydrocarbons (UHC). In this study, the sources of UHC of a low temperature combustion system were investigated in both a standard, all-metal single-cylinder Diesel engine and an equivalent optically-accessible engine. The investigations were conducted under low load operating conditions (2 and 4 bar IMEP). Two piston bowl geometries were tested: a wall-guided and a more conventional Diesel chamber geometry. Engine parameters such as the start of injection (SOI) timing, the level of charge dilution via exhaust gas re-circulation (EGR), intake temperature, injection pressure and engine coolant temperature were varied. Furthermore, the level of swirl and the diameter of the injector nozzle holes were also varied in order to determine and quantify the sources of UHC.
Technical Paper

Simulation of Urea-SCR Process Applied to Lean-burn SI Engines

2009-11-02
2009-01-2776
Lean-burn combustion in SI engines can significantly reduce fuel consumption but NOx reduction becomes challenging because classic three-way catalyst (TWC) is no more efficient. Urea-SCR is then an interesting alternative solution because of its high NOx conversion efficiency without any additional fuel consumption. The coupling between two SI lean-burn engines (stratified and homogeneous combustion) and a urea-SCR catalyst was simulated on the NEDC cycle. Simulation results showed that the SCR efficiency would comply with the limits required by future Euro 5/6 regulations. Associated urea solution consumptions were estimated thanks to a simplified model. Finally, a comparison with a Diesel application was also made. It showed that the required amount of reducing agent remained significantly higher for SI lean-burn engines than for Diesel engine.
Technical Paper

SCR for Passenger Car: the Ammonia-Storage Issue on a Fe-ZSM5 Catalyst

2009-06-15
2009-01-1929
A comprehensive experimental approach has been developed for a Fe-ZSM5 micro-porous catalyst, through a collaborative project between IFP, PSA Peugeot-Citroën and the French Environment and Energy Management Agency (ADEME). Tests have first been conducted on a synthetic gas bench and yielded estimated values for the amount of NH3 stored on a catalyst sample. These data have further been compared to those obtained from an engine test bench, in running conditions representative of the entire operating range of the engine. 15 operating points have been chosen, considering the air mass flow and the exhaust temperature, and tested with different NH3/NOx ratios. Steady-state as well as transient conditions have been studied, showing the influence of three main parameters on the reductant storage characteristics: exhaust temperature, NO2/NOx ratio, and air mass flow.
Journal Article

A Comparison of Combustion and Emissions Behaviour in Optical and Metal Single-Cylinder Diesel Engines

2009-06-15
2009-01-1963
Single cylinder optical engines are used for internal combustion (IC) engine research as they allow for the application of qualitative and quantitative non-intrusive, diagnostic techniques to study in-cylinder flow, mixing, combustion and emissions phenomena. Such experimental data is not only important for the validation of computational models but can also provide a detailed insight into the physical processes occurring in-cylinder which is useful for the further development of new combustion strategies such as gasoline homogeneous charge compression ignition (HCCI) and Diesel low temperature combustion (LTC). In this context, it is therefore important to ensure that the performance of optical engines is comparable to standard all-metal engines. A comparison of optical and all-metal engine combustion and emissions performance was performed within the present study.
Journal Article

Advanced Injection Strategies for Controlling Low-Temperature Diesel Combustion and Emissions

2009-06-15
2009-01-1962
The simultaneous reduction of engine-out nitrogen oxide (NOx) and particulate emissions via low-temperature combustion (LTC) strategies for compression-ignition engines is generally achieved via the use of high levels of exhaust gas recirculation (EGR). High EGR rates not only result in a drastic reduction of combustion temperatures to mitigate thermal NOx formation but also increases the level of pre-mixing thereby limiting particulate (soot) formation. However, highly pre-mixed combustion strategies such as LTC are usually limited at higher loads by excessively high heat release rates leading to unacceptable levels of combustion noise and particulate emissions. Further increasing the level of charge dilution (via EGR) can help to reduce combustion noise but maximum EGR rates are ultimately restricted by turbocharger and EGR path technologies.
Technical Paper

Ethanol as a Diesel Base Fuel: Managing the Flash Point Issue - Consequences on Engine Behavior

2009-06-15
2009-01-1807
Facing more and more stringent regulations, new solutions are developed to decrease pollutant emissions. One of them have shown promising and relevant results. It consists of the use of ethanol as a blending component for diesel fuel Nevertheless, the addition of ethanol to Diesel fuel affects some key properties such as the flash point. Consequently, Diesel blends containing ethanol become highly flammable at a temperature around ambient temperature. This study proposes to improve the formulation of ethanol based diesel fuel in order to avoid flash point drawbacks. First, a focus on physical and chemical properties is done for ethanol based diesel fuels with and without flash point improvement. Second, blends are tested on a passenger car diesel engine, under a wide operating range conditions from low load low speed up to maximum power. The main advantage of the ethanol based fuels generate low smoke level, that allows using higher EGR rate, thus leading to an important NOx decrease.
Technical Paper

Detailed Particulate Characterization from HCCI Combustion for Future DPF Development

2009-04-20
2009-01-1185
This paper presents the detailed characterization of particulate emissions from a NADI™ dual mode engine (HCCI at low load and conventional combustion at high load). Morphology, composition and chemical reactivity of the particulate matter generated on an engine running in HCCI mode have been specified and compared to the conventional mode reference. Results showed that HCCI combustion formed particles with a higher volatile organic fraction due to the relatively high level of HC generated by this kind of combustion. Advanced soot characterization emphasized that HCCI soot is oxidized at a slower reaction rate than conventional soot, but with a lower temperature. This last characteristic could partially compensate the poor continuous regeneration effect due to low NO2 emission levels observed in HCCI combustion. Microscopic observation and particle sizing did not show significant differences between HCCI and conventional soot.
Technical Paper

Generating Thermal Conditions to Regenerate a DPF: Impact of the Reductant on the Performances of Diesel Oxidation Catalysts

2009-04-20
2009-01-1085
The influence of the type of fuel and the feeding means to a DOC, in order to regenerate a DPF, was investigated. Diesel fuel in cylinder late post-injection was compared to the injection in the exhaust line, through an exhaust port injector, of diesel fuel, B10 (diesel fuel containing 10% of esters) and gasoline. Diesel fuel exhaust injection resulted in a deteriorated conversion efficiency, while the incorporation of esters to the diesel fuel was demonstrated to have no influence. Gasoline exhaust injection led to less HC slip than diesel fuels. Temperature dynamics resulting from injection steps showed taught that the shorter the hydrocarbons (within the tested fuels), the slower the response. These differences can be caught by simple models, leading to interesting opportunities for the model-based control of the DPF inlet temperature during active regenerations.
Journal Article

Study of the Mixing and Combustion Processes of Consecutive Short Double Diesel Injections

2009-04-20
2009-01-1352
The mixing and combustion processes of short double Diesel injections are investigated by optical diagnostics. A single hole Common Rail Diesel injector allowing high injection pressure up to 120MPa is used. The spray is observed in a high pressure, high temperature cell that reproduces the thermodynamic conditions which exist in the combustion chamber of a Diesel engine during injection. Three configurations are studied: a single short injection serving as a reference case and two double short injections with short and long dwell time (time between the injections). Several optical diagnostics were performed successively. The mixing process is studied by normalized Laser Induced Exciplex Fluorescence giving access to the vapor fuel concentration fields. In addition, the flow fields both inside and outside the jets are characterized by Particle Imaging Velocimetry.
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